Since you are replacing all of the smoke alarms, use the same brand. Note the installation guidelines as to distance from walls, ceilings, corners. Note that there is a limit to the number of alarms that can be interconnected. Get alarms with a hush button and a 10 year battery. In Oreogn, that is a requirement. Home Cheapo, a devision of China, inc, tends to ignore that requirement. An earlier poster said the red wire is the interconnect, some alarms use an orange wire or yellow wire. Make sure the power is off before playing with electricity.